Dear Readers, the London Natural History talk this week was of particular interest to me. When we had a bird survey done in 2019, Coldfall Wood was found to be particularly rich in breeding birds for an urban woodland, but the increased footfall during lockdown, coupled with the threats to the environment itself, have made me worry about the additional pressure that is being put on the animals and plants that live there.
Jeff Waage was part of a team that undertook a survey of Hampstead Heath last year. Part of the reason was to determine which birds were displaying breeding activity, and where: disturbance from walkers and dogs is widespread even if there isn’t a pandemic, and there has been an increased demand for Forest Schools, ‘Forest Bathing’ and professional dogwalking. In the past year the Heath has had an estimated 50 million visitors, which is pretty much equivalent to most of the population of the country popping in. But data can help, and so Waage and his team walked transects of between 1 and 3 kilometres through the Heath on at least six occasions, looking for breeding behaviour.
Kenwood, Hampstead Heath (Photo One)
Breeding behaviour was defined as territorial singing, birds carrying nesting material or food or fecal sacs, birds actually sitting on a nest, territorial disputes or sightings of fledglings. In my experience birds are very good at hiding nests, but you can fairly easily spot them ‘eating for two’ (or a dozen in the case of blue tits).
At the end of the survey, there had been 2169 sightings of 41 species of bird. Compared with the 26 species seen in Coldfall Wood this probably sounds pretty good, but the Heath has a much wider range of habitats. However, it’s clear that the Heath’s biodiversity has been under stress for some time: in 1992, a survey revealed 71 species. Many of those lost have been ground nesting birds, who are always the first victims of too much footfall and too many dogs, but even birds such as the mistle thrush and the common whitethroat appeared to be in decline.
Common Whitethroat (Curruca communis) (Photo Two)
Waage estimated that 40% of the Heath’s bird species were red or amber listed: he explained that this designation was arrived at by looking at both the vulnerability of the species (i.e. was it nesting in an area of high disturbance) combined with its ‘patchiness’ (i.e. were there just a few isolated populations within the Heath). For example, the whitethroats nested in scrubby areas where there was a lot of picnicking and dog walking, and there appeared to be only one pair of sparrowhawks.
The approach to maintaining and increasing the bird biodiversity of the Heath was multi-pronged.
Firstly, there was a need to identify areas of the Heath where there would be the least impact on breeding birds for commercial activities such as the forest schools, and this was possible following the survey.
Secondly, where birds were vulnerable there was to be a bid to raise public awareness, through new signage and articles in local newspapers.
A third area was to improve and even create habitat, such as reed beds for reed buntings.
Finally, resources such as food and nest boxes could be made available.
There was also a need to investigate what was happening on the fringes of the Heath – there were surprisingly few nesting finches, for example, and the group felt that this was probably because the finches were nesting in local parks and gardens instead, where there was a higher availability of food.
And lastly, and probably most importantly, the Heath needs continued monitoring to see what’s happening with the bird populations. Data can be our most powerful tool in gaining an understanding of what’s happening in an area, and over time. It will be interesting to see what future surveys reveal.
I’ve always been very happy to just enjoy nature, and to be thrilled at the arrival of a new bird or the sight of an unexpected insect. I’m still thrilled, but it seems to me that collecting data is a way of putting meat onto the bones of the anecdotal picture that you build up over the years. Citizen science is becoming increasingly popular, and I hope that, just as the Big Garden Birdwatch has become a major way of recording trends in garden birds, so other surveys will build up a picture of what’s going on with other plants and animals. In fact, there’s an online conference on this very subject being run by the Field Studies Council in May, with the added bonus that it’s concentrating on urban wildlife recording. I’ll be there, and will report back, but for £5 it seems like a bargain for anyone interested in getting involved with recording. With habitat destruction and climate change in full swing there has never been a better time to take notice of what’s going on around us.
Dear Readers, can I start by saying that this was a fascinating and well-presented talk, with lots of fascinating videos and graphics, and if you have an hour to spare I would hot-foot it over to the LNHS Youtube channel to watch the whole thing. Steve Portugal is such a clear and entertaining speaker that it’s best to get this info direct, but here is my synopsis.
The talk is really about why birds gather in groups, how they behave when they do, and what advantages they gain from their behaviour. There are two main ways of ‘flocking’, and these are dictated largely by size. A bird that is smaller than a black-headed gull is likely to form a ‘cluster’ – we see this in pigeons and starlings and all those other little birds. Any bird larger than this is likely to fly in a V-formation, so that includes cranes, geese, pelicans, flamingoes and, as we’ll see, ibises.
To start with, Portugal looked at birds that fly in a V-formation. Partly this might be because large birds are much less manoeuvrable – a crane has the same turning circle as a jumbo jet, apparently. Other reasons might be:
the dilution effect – if lots of birds fly together, an individual is less likely to be predated (this applies to cluster flocks too)
Navigation – older, more experienced birds fly at the front to teach the younger birds behind the route.
Vision – it’s easier to see the lead bird if you fly in a V formation
Energetic – birds are able to save energy by flying in this way.
It’s this last point that Portugal is most interested in. When a plane or a bird flies, it pushes the air in front of it out of the way. At the wing-tip something called a wing-tip vortex is created, and this provides an updraft, which makes staying in the air easier. However, most of the air gets pushed down and creates a downdraft, which will push anything following down. It’s this effect that dictates the gap between planes when taking off at an airport, and its the wingtip vortex effect that is thought to be one of the reasons why birds fly in a V formation.
Lest you think that this is all about birds, Portugal explained that aircraft manufacturers are desperate to copy this effect, to save fuel. He showed a short film made by an airline in which a plane takes off from Melbourne and is joined by others from other Australian airports to fly across the Pacific. When the planes join, they get into a V formation, and fly together until they make landfall above the US, at which point the planes peel off to go to their different destinations. However, another film showed a group of small planes trying to do just this, and getting into all kinds of trouble – planes have to get so close together to find the updraft from the wingtip that they risk stalling or tumbling over. It’s thought that only a computer will be able to calculate the manoeuvres required with enough accuracy to avoid disaster.
The Red Arrows display team in a V Formation. Not as easy as it looks! (Photo One)
However, back to the birds. Portugal’s subject study was made possible by the advent of biologgers that are small and light enough to attach to a bird, and also by a study into the Waldrapp Ibis (also known as the Northern Bald Ibis). Historically they were present all through Mediterranean Europe, Northern Africa and the Middle East but, after the recent extinction of the Syrian population, the only wild birds left are in Morocco. This population doesn’t migrate, but it was hoped that they could be trained to return to their old haunts and establish new groups in Europe. To do this, the birds were given a human foster parent, who lived with them for nine months. Then, they were trained to fly after a microlite, and were eventually taught a migration route to Northern Italy.
Waldrapp Ibis (Geronticus eremita) (Photo Two)
What Portugal found was that these birds, who had human ‘parents’, automatically formed a V Formation when they flew, at 45 degrees to one another, approximately 1.2 metres apart. This was exactly as predicted by aerodynamic theory, which is based on fixed-wing planes. What the birds did was synchronise their wingbeats naturally to avoid generating turbulence between them. Each bird except the one right at the front rode on the updraft of the bird in front.
The group was dynamic, with no clear leader, though birds did seem to have a preference for their position, be it to the right or left, front or back.
However, the birds noticed how long another bird took at the front of the flock, and would then allow it to take a rest at the back, as if they had an innate sense of fairness.
What happened in the flock also depended on the ‘popularity’ of the individual bird. Portugal defined this as ‘the number of connections and interactions’ that a bird had with other birds. If an ‘unpopular’ bird stopped off for a rest, the others would look round, notice who it was, and then just keep going. If a ‘popular’ bird stopped, however, all the other birds would go down for a rest too. What we think of as ‘leadership’ might just be about a network of relationships instead.
Waldrapp Ibis in flight (Photo Three)
Portugal finished his talk with something a bit closer to home: pigeons. Pigeons are about the maximum size for birds that fly in a cluster, and, unlike V Formation flying, being at the front of the group is good from an aerodynamic point of view, being at the back is bad.
Sadly, in pigeon society the popular/unpopular thing plays out in a different way. Shy pigeons are nearly always at the back. Bold, investigative pigeons are nearly always at the front. And unlike with geese and cranes, that’s the way it stays – if you’re a backmarker, that’s where you’ll stay.
Portugal had his pigeons fly over a number of routes. To start with, the group would be somewhat inefficient, but after a dozen flights they’d have the most direct route mapped, and that would be the one that they’d always follow. However, here’s the rub. After the flock had flown a route over a hundred times, he would take pigeons out for a solo flight. The ones who were always at the front came home pretty directly (though interestingly the flock as a whole always flew faster than a solo bird). But when he released a bird that had been at the back of the flock, they almost always either gave up and went to sit in a tree, or got lost, sometimes for days.
Were they just not paying attention? Or were they so intent on keeping up that they didn’t have the energy to see where they were going? Could they maybe not see the lead bird properly? All very good questions for which we have no answers. But how fascinating! I learned so much from this talk, and in particular I loved the clear structure, which makes it so much easier to take in and to remember – I’ve barely had to look at my notes while I’ve been writing this. Do pop over and have a look. I guarantee that you won’t be disappointed.
Dear Readers, this talk exemplified why I am loving this series so much. James Heal is such an enthusiast that although I knew next to nothing about plant galls at the beginning, by the end I was desperate for spring to come so that I could go out gall-hunting. Heal endeared himself to me greatly by saying that he had a dream of giving up his job in finance so that he could become a gall-mite specialist. Who wouldn’t rather be a gall-mite specialist is my question, and I’m an accountant too. But let’s see first of all what a gall is.
We’ve all probably seen plant galls, even if we haven’t been aware of it.
Silk button spangle galls on oak (Photo One)
A gall is abnormal growth on a plant under the influence of another organism. So the ‘silk buttons’ above are actually created by the plant itself, due to chemicals produced by the invading organism. The gall involves the enlargement or proliferation (or both) of the cells or vascular tissue of the plant. This is produced for the nutrition and protection of the gall-inducing organism.
Knopper gall on oak (Photo Two)
The great thing about galls (or one of the great things) is that they can be used to identify what caused them. Gall midges, for example (of which more later) are extremely difficult to identify to a species level from the insect, but the galls can be diagnostic.
So, how do you know what gall you’re looking at? Heal suggested a three-part approach:
Firstly, identify your plant. This might seem easy (‘It’s an oak’) but what kind of oak is it? There are some galls that we’ve all seen on lime leaves, even if we didn’t know what they were, but to identify the insect that caused them we need to know if we’re looking at a small-leaved lime, a broad-leaved lime or the very common hybrid between the two. Why is life never simple, I ask myself. Probably because it would be boring.
Having identified your species, it makes sense to take a good detailed note of where exactly on the plant you found the gall – leaf rib, body of the leaf, stem, bud?
Secondly, take a number of photos (if it’s a leaf, take both sides). If you can zoom in or magnify, that’s a good idea too. Many galls can be identified right down the species just through a good photo. If you want to become a serious galler (or Cecidologist) you might consider taking specimens and even rearing the inhabitants of the galls until they emerge, blinking, into the big wide world, but it’s not necessary for most people.
Thirdly, get yourself a good guide. If you are just beginning, Heal recommends this one:
But if you’re more serious, this is the one to go for, and apparently a new edition is due out soon.
And if you are really, really serious, the New Naturalist on plant galls has everything you ever wanted to know. This one is, I think, out of print, but you can get one-off reprints of New Naturalists if you go to their website, or second-hand bookshops will often have them. After all, plant galls are not the most apparently interesting of subjects, though after Heal’s talk I imagine there might be a run on the title.
Then, Heal moved on to talk about the different organisms that cause galls, and there are a fair few of them. After all, if you are a delicate little larva, how nice it must be to be surrounded by a robust protective covering while you munch away to your heart’s content, and many unrelated insect groups have taken this route.
First, we have the gall midges (Cedidomyiidae), members of the fly family (Diptera). These are tiny creatures, many of whom are less than a millimetre long. They have these remarkable antennae that look like strings of beads. Heal showed a number of photos of the midges causing the leaf to curl around: while we might see the caterpillars of species like the peacock butterfly making themselves a shelter by stitching the leaves of nettles together, with these midges the plant itself is persuaded to grow in an unnatural way. You can see a picture of ash mid-rib gall, caused by a gall midge, below.
Gall midge (Photo Three)
Ash Midrib gall (Photo Four)
Then there are the gall wasps (Cynipidae), who produce some of the most well-known and spectacular galls, such as the oak knopper gall in Photo Two, and the Robin’s pincushion on roses. Within that multicoloured mass of ‘hairs’ is a many-chambered gall, each containing a tiny wasp larvae. Heal points out that if you open up a gall caused by an insect, what pops out might not be the creature that made the gall but another species entirely that is either a parasite, a predator or some other kind of free-loader.
Oyster gall on oak leaf
Then there are the gall mites (Eriophyidae), which are Heal’s favourite group, partly because they are so understudied and so it’s likely that there are some undiscovered species lurking in our back yards. They are not typically ‘mite-y’ looking, but, as Heal put it, they look more like carrots, long and slim. The gall that you might have seen most often is the Nail gall on lime leaves, which is rather beautiful in my opinion. Some of the galls contain microscopic ‘hairs’ which can be diagnostic for species. Some gall mites are pests of food crops, but others, such as the bindweed gall mite, are used for biological control of noxious weeds.
Lime Nail Gall (Photo Six)
A cereal rust mite (Photo Seven)
So, these are the three main groups of insects who can create galls, but there are many others; sawflies on willow, aphids on elm and some species of moth. Then there are the fungi that can induce galls. Mistletoe technically is a gall-causer – the tree produces distortion and swelling at the point of infection, induced by the parasite. And then there are endless bacteria and viruses that can cause galls.
Galls on crack willow caused by a sawfly (Photo Eight)
So this was a most interesting talk by James Heal – he pitched it perfectly for beginners, I wouldn’t be the least bit surprised if a whole new bunch of gallers has been inspired by his presentation. I certainly learned a lot, and it’s left me with a whole lot of things to ponder. If you’d like to listen to the whole thing (which I would recommend) you can find the link here.
Photo One by Lairich Rig / Silk button spangle galls on oak
Dear Readers, this week’s talk was by David Humphries, Tree Management Officer for the City of London. He has been based in Hampstead Heath for 35 years, and recently won a special award for caring for London’s trees. I was really looking forward to this talk, and I wasn’t the only, as for the first time since the LNHS talks started, this one was sold out! Fortunately, you can still watch the whole thing here, and I’d recommend that you do so, as the photos were fantastic, and I can only capture the merest flavour of the range of the talk.
Humphries is something of a fungiphile: he gave us a quick look at his computer, where he has 22,000 photos of fungi, neatly arranged into 584 folders, one for each species. Most of them were taken on Hampstead Heath, which has over 25,000 trees, and where upwards of 600 fungal species have been recorded. Humphries thinks this is probably because, unlike in 1830 when John Constable painted a view of the Heath that shows it completely bereft of trees, there are now a substantial number of habitats and tree species.
First, we had a quick run through the variety of fungi that can be found in association with trees. There are the perennial bracket fungi such as hoof fungus (Fomes fomentarius) which persist for years. They form layers, as you can see from the photo below, but these are not necessarily annual – each layer is created when the fungus produces spores, and in one example that Humphries showed us later in the talk, it’s clear that they can be produced on multiple occasions in a single year if the conditions are right.
Incidentally, Otzi the iceman who was retrieved from a glacier in Austria and turned out to be about 5000 years old had some pieces of hoof fungus in his bag – it is used to produce amadou, which can be used as tinder. But as usual I digress.
Hoof fungus (Fomes fomentarius) (Photo One)
Then there are the annual bracket fungi, such as shaggy bracket (Inonotus hispidus) which produce fruiting bodies and spores and then die every year. They may remain in the same location for many years, and on the photos that Humphries shared you could see the scars of the previous generations on the bark.
Shaggy bracket (Inonotus hispidus) (Photo Two)
However, with so many types of fungi, many looking superficially the same, how to ID them to species level? For some, you have to use microscopy of the spores, but Humphries had some general tips:
Take a slice through the fungus to look at the spore layer and the flesh
Have a look at the spore colour – anything from white to saffron to darkest inky black
Look in detail at the spore layer to see how the tubes from which the spores are released are coloured and shaped – Humphries recommended two useful resources:
If you are looking at a more typical ‘mushroom’, look at the gills and check to see whether they are attached to the stem or not (the word for where gills do form part of the stem is ‘decurrent’, a new word for me!)
Then, we moved on to the three ways in which fungi can be associated with trees.
Parasitic – it was Humphries view that parasitic fungi start to become problematic when a tree is weakened, either. A typical example would be honey fungus (Armillaria mellea)
Honey Fungus (Armillaria mellea) (Photo Three)
Saprophytic – fungi that feed on fallen leaves, dead branches etc. They recycle nutrients that would otherwise not be released back into the soil. The earthstar that I found in St Pancras and Islington Cemetery would be an example.
And finally, there are the Mycorrhizal fungi. It’s only recently that we’ve learned what a vital part these fungi play in the health of plants – they form a mutualistic relationship with the roots of trees in this case, vastly extending the range of the roots in return for some of the benefits of photosynthesis. Some very familiar fungi, such as the edible boletus mushrooms and the traditional ‘toadstool’, Amanita muscari, are examples of mycorrhizal fungi. The fruiting bodies can often be seen exactly following the lines of the roots of the trees that are hosting them.
Amanita muscaria (Photo Four)
Humphries has, as you might expect, found some very interesting fungi in Hampstead, and one of the most attractive is the Many-Zoned Rosette (Podoscypha multizonata), of which the UK has about 80% of the European population. This is a rare species, which is being assessed by the IUCN for the Global Fungal Red List, and one reason for its rarity is that it is normally found on veteran oaks in oak pasture, a vanishingly rare habitat in the UK (though as I’m currently reading in Isabella Tree’s ‘Wilding’, it was probably once much more common. However, Humphries has noticed that the fungus has increased its range of hosts to include beech, hornbeam, lime, red and turkey oak and even horse chestnut, so maybe this bodes well for its future.
As you might expect from someone who is involved in maintaining the health of trees, Humphries has a lot of interesting things to say about the different ways that fungi can infiltrate a tree. There are broadly three colonisation strategies.
The first is fungal-induced dysfunction, as favoured by our old friend honey fungus. Basically, rhizomorphs, which are a ‘rope’ of hyphae (the filaments of the fungi) travel through the soil and colonize a tree which already weakened. Once they’ve found such a tree, they fan out under the bark and infiltrate the vascular system, preventing the tree from transporting water and nutrients. In honey fungus the rhizomorphs are often called ‘bootlaces’ and you can see why.
Honey fungus rhizomorphs (Photo Six)
Secondly, some fungi infiltrate the sapwood when it’s suddenly exposed, whether by storm damage, lightning, injudicious pruning, or, in the case of the poor tree on my road, sudden collision with a skip. Examples include the beefsteak fungus, which at least has the benefit of being edible.
And finally, there are the fungi that are living in the tree already, but which can only proliferate when the tree is weakened (endophytic fungi). These remind me a bit of the bacteria that live happily on our skin for ages, until our immune systems take a knock and then they lurch into action (Staphylococcus springs to mind). An insect attack, storm damage, root rock in high winds can all be starting points for such fungi (one example would be the birch polyphore (Fomitopsis betulinus). Humphries noted how, when a tree is cut down, these fungi can appear remarkably quickly once the sapwood is exposed to the air.
Trees can live quite happily with fungal infestations, sometimes for decades. However, many fungi will eventually cause problems. Some cause white rot, which is where the wood turns white and spongy because the fungus has ‘eaten’ the lignin which provides stability – this is what honey fungus does. Some cause brown rot, which is where the cellulose is ‘eaten’ instead, and the tree becomes brittle – an example of this would be chicken of the woods (Laetiporus sulphureus). Some trees will eventually be hosts to both. And it isn’t just trees in forests, either.
Chicken of the woods (Laetiporus sulphureus) (Photo Nine)
Humphries mentioned two fungal diseases that are affecting that icon of the capital, the London Plane (Platanus x hispanica). One is Massaria Disease, caused by the fungus Splanchnonema platani. Humphries is of the opinion that this used to largely appear during droughts, but as most street trees have roots that are compacted, and as climate change affects rainfall in unpredictable ways, it has been seen in the UK. It normally causes branch fall in trees over 40 years old.
The second is elbowpatch crust (Fomitiporia punctata). According to the Forest Research UK site, this seems to affect a particular clone of the London Plane which has a propensity to develop weak forks. When infected by the fungus, it can drop whole branches, which is something of a health hazard considering how many there are.
Humphries spent some time explaining how part of his work is assessing trees, and deciding whether or not to save them, and how. There are various techniques that can be used to assess the amount of damage – a microdrill can be used to take a core through the tree without harming it, to see how far any rot has progressed. The whole tree can also be fitted with what sonic tomography receivers, which used sound waves to detect the integrity of the trunk – the photo of the tree in Humphries’s photo makes it look rather as if it’s getting an ECG. And there is much that often can be done, in terms of reducing the wind load that the plant has to bear in storms to prevent it being knocked over, and to support the tree. However, when the worst comes to the worst, the standing wood is endlessly useful for everything from beetles to woodpeckers, and fungi themselves are food for many invertebrates and other creatures (I’ve even watched a fox take a speculative bite out of a puffball.
However, the lockdowns and the increased footfall in Hampstead have caused additional challenges for fungi, and for the people who care about them. The big enemy seems to be compaction of the soil – no one seems to know how much this will damage the underground hyphae of the mycorrhizal fungi, without which many of the trees on the Heath will no longer thrive. Soil health is an issue for all of us, wherever we are, and it’s something to which we pay far too little attention in my view. I worry about the trampling in my local wood, but am also uncertain what we can do about it.
I really recommend this talk. It was stuffed full of information, and some of the photos that Humphries presented were wonderful. I learned so much, and I think I’ll probably watch it again to pick up some of the things that I missed or didn’t understand the first time round. So if you have an hour to spare and are wondering what to do during lockdown, here’s something to keep you entertained (along with all the other LNHS talks). The amazing world of fungi awaits!